WASHINGTON, March 15 (UPI) -- U.S. researchers are trying to understand why so many gorillas in North American zoos are dying of heart disease.

WASHINGTON, July 2 (UPI) -- An attempt to implant a pacemaker-like device in a western lowland gorilla at Washington's National Zoo ended when the 23-year-old male died in surgery.

WASHINGTON, Oct. 6 (UPI) -- National Zoo veterinarians in Washington have performed a tumor operation on the head of a giraffe, a difficult operation hailed as a first.